Submitted to: Clay International Conference Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 6/15/1997
Publication Date: N/A
Technical Abstract: Association processes between soil colloidal components may influence the sorptive capacity of individual constituents. In this work, the sorption- desorption of the s-triazine herbicides atrazine and simazine on binary and ternary model associations of montmorillonite, ferrihydrite and humic acid was determined using the batch equilibration procedure. Results were compared with sorption-desorption on the single model constituents. Iron species and humic substances coatings on the montmorillonite increase the sorption of the herbicides on the clay. Protonation of atrazine and simazine catalyzed by hydroxy iron polymers and acidic functional groups of humic acid on the surface of montmorillonite is proposed to be responsible enhanced sorption on the clay. Ferrihydrite-humic acid complexes also sorb more s-triazine herbicides than ferrihydrite without humic acid, although some surface of the humic acid is blocked after its association with the iron oxyhydroxide. Sorption studies of atrazine and simazine on a clay- ferrihydrite-humic acid model soil aggregate indicate that humic substances can hinder the access of herbicide molecules to iron species coatings on montmorillonite, especially if there is a high interaction organic matter- iron coated clay. Sorption-desorption of atrazine and simazine by the sorbents studied was found to be reversible.